Inspirated by some promo cards (though I never played with them, the only games I played were on BrettSpielWelt and a bit IRL), I give some ones.
Card : "Black market".
It has a number 25. If both this and the 25 plant are present, it is ranked on the higher side (closer to future market than actual market).
During the resource buy phase, if you have it, you can buy stuff from the supply, each unit for $2 less than its actual cost (by cost I mean the lowest cost on the board) but not less than $1. For example, if you have a plant that can store 6 coal and minimal cost of coal is $4, you can buy 6 coals at $2 each. You can buy independently from regular market or black market.
When it is available during the auction phase, you may bid it, regardless it's on the actual or future market. At the end of the bid-phase it is available, it is automatically removed from the game if it hasn't been purchased.
It doesn't count in the limit of plants you can have.
Card : "Illegal plant"
Let's assume a plant that is really strong, but that is far too polluting, or something else...
It is a plant numbered 20 (coming after the regular 20 plant), produces 6 for nothing just like the 50 plant... BUT : it is banned, as it doesn't respect the norms. And when step 3 starts, you must discard this plant AND pay a $100 (for instance) fee if you have it (or everything if you don't have enough), because you don't want to have problems with authorities ! During bureaucracy phase, you can choose to discard it and benefit of 3 supplied cities for this turn only instead of the usual 6.
If it should be put to bottom of deck during steps 1 and 2 as the highest plant on the board, it is removed from the game instead, and this counts as a "card put to bottom" for this turn.
If the game ends while in step 2, this still counts for providing 6 cities.
AAAND I forgot : at start of step 3, if it is present on the board, it is imediatly removed and replaced. If step 3 card is revealed during bid phase, this means nobody should buy this, and it will remain until end of phase, when step 3 starts.
Thoughts, anybody ?